Long-term treatment with responsive brain stimulation in adults with refractory partial seizures

Electrocorticographic events from long-term ambulatory brain recordings can potentially supplement seizure diaries

PURPOSE

To determine the feasibility of using epileptiform events detected by continuous electrocorticographic monitoring via a brain-responsive neurostimulation system to supplement patient-maintained seizure diaries.

METHODS

Data were retrospectively analyzed from a randomized controlled trial of brain-responsive neurostimulation (RNS® System) for adjunctive treatment of medically intractable focal onset seizures in 191 subjects. The long-term (≥3 months) correspondence between daily counts of diary-reported seizures and device-recorded "long epileptiform events" (LEs), a proxy for electrographic seizures (ESs), was assessed using cross-correlation and logistic generalized estimating equation models.

RESULTS

Diary-reported seizures and LEs significantly co-varied across days in 124 patients whose detection settings were held constant, with a significantly higher correlation in 54 patients (44 %) whose LEs were usually ESs (high concordance patients). There were more days in which LEs were detected than days in which patients reported a seizure (positive predictive value (PPV): 34 %). On days when there were no LEs, there were typically no diary-reported seizures (negative predictive value (NPV): 90 %). In patients with a high concordance between LEs and ESs, the PPV and NPV were both slightly higher, 43 % (35-52 %) and 93 % (95 % CI: 86-97 %) respectively.

CONCLUSION

Although LEs can substantially outnumber diary reported seizures, the high across-day correlation and strong NPV between LEs and diary seizures suggests that LEs recorded by the RNS® System could potentially supplement seizure diaries by providing an objective biomarker for relative seizure burden.

Mesial temporal resection following long-term ambulatory intracranial EEG monitoring with a direct brain-responsive neurostimulation system

OBJECTIVE

To describe seizure outcomes in patients with medically refractory epilepsy who had evidence of bilateral mesial temporal lobe (MTL) seizure onsets and underwent MTL resection based on chronic ambulatory intracranial EEG (ICEEG) data from a direct brain-responsive neurostimulator (RNS) system.

METHODS

We retrospectively identified all patients at 17 epilepsy centers with MTL epilepsy who were treated with the RNS System using bilateral MTL leads, and in whom an MTL resection was subsequently performed. Presumed lateralization based on routine presurgical approaches was compared to lateralization determined by RNS System chronic ambulatory ICEEG recordings. The primary outcome was frequency of disabling seizures at last 3-month follow-up after MTL resection compared to seizure frequency 3 months before MTL resection.

RESULTS

We identified 157 patients treated with the RNS System with bilateral MTL leads due to presumed bitemporal epilepsy. Twenty-five patients (16%) subsequently had an MTL resection informed by chronic ambulatory ICEEG (mean = 42 months ICEEG); follow-up was available for 24 patients. After MTL resection, the median reduction in disabling seizures at last follow-up was 100% (mean: 94%; range: 50%-100%). Nine patients (38%) had exclusively unilateral electrographic seizures recorded by chronic ambulatory ICEEG and all were seizure-free at last follow-up after MTL resection; eight of nine continued RNS System treatment. Fifteen patients (62%) had bilateral MTL electrographic seizures, had an MTL resection on the more active side, continued RNS System treatment, and achieved a median clinical seizure reduction of 100% (mean: 90%; range: 50%-100%) at last follow-up, with eight of fifteen seizure-free. For those with more than 1 year of follow-up (N = 21), 15 patients (71%) were seizure-free during the most recent year, including all eight patients with unilateral onsets and 7 of 13 patients (54%) with bilateral onsets.

SIGNIFICANCE

Chronic ambulatory ICEEG data provide information about lateralization of MTL seizures and can identify additional patients who may benefit from MTL resection.

Electrical cortical stimulation for treatment of intractable epilepsy originating from eloquent cortex: surgical accuracy and clinical efficacy

BACKGROUND

Electrical cortical stimulation is shown effective in treating patients with drug-resistant epilepsy. We demonstrated how detailed procedures of pre- and intra-operative planning of cortical stimulation implantation may influence the results of seizure reduction rate.

METHODS

To confirm the precision of subdural grids covering the epileptogenic foci in the eloquent regions, pre- and intra-operative video-electroencephalography (VEEG) were performed in patients with drug-resistant epilepsy during a 4-day 24-h monitoring. The localization of the grid was determined via 3D reconstruction imaging of subdural electrodes co-registered onto the patient's cortex. A final quadripolar lead in cyclic stimulation mode was then placed and secured on the target cortex area. Post-operative 3D CT ensured the accurate location of stimulation lead without any misplacement. Bipolar cyclic stimulation and post-implantation VEEG were performed for 7 days. Patients were discharged and followed up regularly for parameters adjustment and recording of seizure outcomes.

RESULTS

Eight patients received chronic cortical stimulation implantations between February 2003 and December 2017. The mean age of these patients was 21.1 years old and the average post-operative follow-up was 77.3 months. Comparisons of their seizure frequency at baseline and during the postoperative period revealed a mean reduction in seizures of 60.4% at the first year and 65.6% at the second year.

CONCLUSIONS

Pre-surgical planning enhanced the accuracy of electrode placement and led to a favorable seizure reduction rate. Our report confirms that electrical cortical stimulation with detailed implantation procedures is safe and effective for patients with drug-resistant epilepsy originating from eloquent cortex.

The role of devices in managing risk

Over the last few years, there has been significant expansion of wearable technologies and devices into the health sector, including for conditions such as epilepsy. Although there is significant potential to benefit patients, there is a paucity of well-conducted scientific research in order to inform patients and healthcare providers of the most appropriate technology. In addition to either directly or indirectly identifying seizure activity, the ideal device should improve quality of life and reduce the risk of sudden unexpected death in epilepsy (SUDEP). Devices typically monitor a number of parameters including electroencephalographic (EEG), cardiac, and respiratory patterns and can detect movement, changes in skin conductance, and muscle activity. Multimodal devices are emerging with improved seizure detection rates and reduced false positive alarms. While convulsive seizures are reliably identified by most unimodal and multimodal devices, seizures associated with no, or minimal, movement are frequently undetected. The vast majority of current devices detect but do not actively intervene. At best, therefore, they indicate the presence of seizure activity in order to accurately ascertain true seizure frequency or facilitate intervention by others, which may, nevertheless, impact the rate of SUDEP. Future devices are likely to both detect and intervene within an autonomous closed-loop system tailored to the individual and by self-learning from the analysis of patient-specific parameters. The formulation of standards for regulatory bodies to validate seizure detection devices is also of paramount importance in order to confidently ascertain the performance of a device; and this will be facilitated by the creation of a large, open database containing multimodal annotated data in order to test device algorithms. This paper is for the Special Issue: Prevent 21: SUDEP Summit - Time to Listen.

Post-placement Lead Deformation Secondary to Cerebrospinal Fluid Loss in Transventricular Trajectory During Responsive Neurostimulation Surgery

Responsive nerve stimulation (RNS) represents a safe and effective treatment option for patients with medically refractory temporal lobe epilepsy. In cases of long intraparenchymal course and posterior-anterior electrode direction through occipital burr holes, disciplined stereotaxy is essential for stimulation of the appropriate target.

A 13-year-old female with a history of multifocal, independent, bitemporal-onset seizures since 12 months of age showing evidence of left-sided mesial temporal sclerosis on MRI, underwent placement of bilateral mesial temporal RNS leads. An O-arm spin was performed after the placement and the images obtained were fused to the preoperative CT images. It demonstrated curvature of the leads, with some deviation from the planned trajectory, but no deviation from the target, that was worse on the left side, compared to the right; the left lead was placed first, followed by the right lead. Following discussion with our epilepsy neurology colleagues in the operating room, electrophysiological measurements from the implanted leads showed cleared epileptic activity and therefore no repositioning was pursued. Our hypothesis at that time was that cerebrospinal fluid leakage distorted the underlying ventricular anatomy causing some curvature in the lead during transventricular course and prolonged consideration during surgery.

In conclusion, transventricular trajectories during RNS lead placement may lead to cerebrospinal fluid loss and associated lead deformation. The distal aspect of the lead may nonetheless reside in the desired surgical target. Neuromonitoring for epileptic signature can provide reassurance with regard to accurate lead placement, obviating the need for lead repositioning. Surgeons should also recognize that fused imaging may confuse inferred anatomic position from preoperative MRI with actual anatomy post brain shift.

Optimizing therapies for neurobehavioral comorbidities of epilepsy using chronic ambulatory electrocorticography

There is an unmet need to improve therapy for neuropsychiatric comorbidities that are highly prevalent in persons with epilepsy (PWE). However, diagnosing and monitoring the neurobehavioral symptoms is challenging as their presentation can overlap with seizures. In this retrospective study, we report the advantage of chronic ambulatory electrocorticography (ECoG) from implanted Responsive Neurostimulator System (RNS®) in characterizing these psychosomatic paroxysms as a possible ictal, postictal, or interictal phenomenon and how the diagnosis guided the therapy choices. Five out of 21 patients with RNS had neuropsychiatric symptoms (panic attack, psychosis, conversion, and somatization disorders) that overlapped with their seizure semiology and were found to benefit from the use of RNS ECoG data by timely diagnosing and titrating targeted therapies. The cases illustrate the use of RNS ECoG data in diagnosing and improving the management of comorbidities in PWE. The ability to access RNS ECoG data and correlate it with patient symptoms is unique among available therapeutic options for PWE.

Early detection rate changes from a brain-responsive neurostimulation system predict efficacy of newly added antiseizure drugs

OBJECTIVE

Brain-responsive neurostimulation (RNS System, NeuroPace) is used to treat medically refractory focal epilepsy and also provides long-term ambulatory neurophysiologic data. We sought to determine whether these data could predict the clinical response to antiseizure drugs (ASDs).

METHODS

First, newly added medications were identified in RNS System patients followed at a single epilepsy center. Daily detection rates including "episode starts" (predominantly interictal activity) and "long episodes" (often electrographic seizures) were compared before and after ASD initiation. Efficacy was determined from documentation of clinical improvement and medication retention. Next, the analysis was repeated on an independent sample of patients from a multicenter long-term treatment trial, using an efficacy measure of ≥50% reduction in diary-recorded seizure frequency after 3 months.

RESULTS

In the single center cohort, long episodes, but not episode starts, had a significantly greater reduction in the first week for clinically efficacious compared to inefficacious medications. In this cohort, having no long episodes in the first week was highly predictive of ASD efficacy. In the multicenter cohort, both long episodes and episode starts had a significantly greater reduction for effective medications starting in the first 1-2 weeks. In this larger dataset, a ≥50% decrease in episode starts was 90% specific for efficacy with a positive predictive value (PPV) of 67%, and a ≥84% decrease in long episodes was 80% specific with a PPV of 48%. Conversely, a <25% decrease in long episodes (including any increase) or a <20% decrease in episode starts had a predictive value for inefficacy of >80%.

SIGNIFICANCE

In RNS System patients with stable detection settings, when new ASDs are started, detection rates within the first 1-2 weeks may provide an early, objective indication of efficacy. These data could be used to identify responses to medication trials early to allow more rapid medication adjustments than conventionally possible.

Responsive neurostimulation for regional neocortical epilepsy

OBJECTIVE

Surgical resection of seizure-producing brain tissue is a gold standard treatment for drug-resistant focal epilepsy. However, several patient-specific factors can preclude resective surgery, including a spatially extensive ("regional") seizure-onset zone (SOZ). For such patients, responsive neurostimulation (RNS) represents a potential treatment, but its efficacy has not been investigated in this population.

METHODS

We performed a multicenter retrospective cohort study of patients (N = 30) with drug-resistant focal epilepsy and a regional neocortical SOZ delineated by intracranial monitoring who were treated with the RNS System for at least 6 months. RNS System leads were placed at least 1-cm apart over the SOZ, and most patients were treated with a lead-to-lead stimulation pathway. Five patients underwent partial resection of the SOZ concurrent with RNS System implantation. We assessed change in seizure frequency relative to preimplant baseline and evaluated correlation between clinical outcome and stimulation parameters.

RESULTS

Median follow-up duration was 21.5 months (range 6-52). Median reduction in clinical seizure frequency was 75.5% (interquartile range [IQR] 40%-93.9%). There was no significant difference in outcome between patients treated with and without concurrent partial resection. Most patients were treated with low charge densities (1-2.5 µC/cm² ), but charge density, interlead distance, and duration of treatment were not significantly correlated with outcome.

SIGNIFICANCE

RNS is a feasible and effective treatment in patients with drug-resistant regional neocortical seizures. Prospective studies in larger cohorts are necessary to determine optimal lead configuration and stimulation parameters, although our results suggest that lead-to-lead stimulation and low charge density may be effective in some patients.

Perspectives on the current developments with neuromodulation for the treatment of epilepsy

Introduction: As deep brain stimulation revolutionized the treatment of movement disorders in the late 80s, neuromodulation in the treatment of epilepsy will undoubtedly undergo transformative changes in the years to come with the exponential growth of technological development moving into mainstream practice; the appearance of companies such as Facebook, Google, Neuralink within the realm of brain-computer interfaces points to this trend.Areas covered: This perspective piece will talk about the history of brain stimulation in epilepsy, current-approved treatments, technical developments and the future of neurostimulation.Expert opinion: Further understanding of the brain alongside machine learning and innovative technology will be the future of neuromodulation for the treatment of epilepsy. All of these innovations and advances should pave the way toward overcoming the vexing underutilization of surgery in the therapeutic armamentarium against medically refractory seizures, given the implicit advantage of a neuromodulatory rather than neurodestructive approach.

Excitation, but not inhibition, of the fastigial nucleus provides powerful control over temporal lobe seizures

KEY POINTS

On-demand optogenetic inhibition of glutamatergic neurons in the fastigial nucleus of the cerebellum does not alter hippocampal seizures in a mouse model of temporal lobe epilepsy. In contrast, on-demand optogenetic excitation of glutamatergic neurons in the fastigial nucleus successfully inhibits hippocampal seizures. With this approach, even a single 50 ms pulse of light is able to significantly inhibit seizures. On-demand optogenetic excitation of glutamatergic fastigial neurons either ipsilateral or contralateral to the seizure focus is able to inhibit seizures. Selective excitation of glutamatergic nuclear neurons provides greater seizure inhibition than broadly exciting nuclear neurons without cell-type specificity.

ABSTRACT

Temporal lobe epilepsy is the most common form of epilepsy in adults, but current treatment options provide limited efficacy, leaving as many as one-third of patients with uncontrolled seizures. Recently, attention has shifted towards more closed-loop therapies for seizure control, and on-demand optogenetic modulation of the cerebellar cortex was shown to be highly effective at attenuating hippocampal seizures. Intriguingly, both optogenetic excitation and inhibition of cerebellar cortical output neurons, Purkinje cells, attenuated seizures. The mechanisms by which the cerebellum impacts seizures, however, are unknown. In the present study, we targeted the immediate downstream projection of vermal Purkinje cells - the fastigial nucleus - in order to determine whether increases and/or decreases in fastigial output can underlie seizure cessation. Though Purkinje cell input to fastigial neurons is inhibitory, direct optogenetic inhibition of the fastigial nucleus had no effect on seizure duration. Conversely, however, fastigial excitation robustly attenuated hippocampal seizures. Seizure cessation was achieved at multiple stimulation frequencies, regardless of laterality relative to seizure focus, and even with single light pulses. Seizure inhibition was greater when selectively targeting glutamatergic fastigial neurons than when an approach that lacked cell-type specificity was used. Together, these results suggest that stimulating excitatory neurons in the fastigial nucleus may be a promising approach for therapeutic intervention in temporal lobe epilepsy.

A Resource-Optimized VLSI Implementation of a Patient-Specific Seizure Detection Algorithm on a Custom-Made 2.2 cm 2 Wireless Device for Ambulatory Epilepsy Diagnostics

A patient-specific epilepsy diagnostic solution in the form of a wireless wearable ambulatory device is presented. First, the design, VLSI implementation, and experimental validation of a resource-optimized machine learning algorithm for epilepsy seizure detection are described. Next, the development of a mini-PCB that integrates a low-power wireless data transceiver and a programmable processor for hosting the seizure detection algorithm is discussed. The algorithm uses only EEG signals from the frontal lobe electrodes while yielding a seizure detection sensitivity and specificity competitive to the standard full EEG systems. The experimental validation of the algorithm VLSI implementation proves the possibility of conducting accurate seizure detection using quickly-mountable dry-electrode headsets without the need for uncomfortable/painful through-hair electrodes or adhesive gels. Details of design and optimization of the algorithm, the VLSI implementation, and the mini-PCB development are presented and resource optimization techniques are discussed. The optimized implementation is uploaded on a low-power Microsemi Igloo FPGA, requires 1237 logic elements, consumes 110 μW dynamic power, and yields a minimum detection latency of 10.2 μs. The measurement results from the FPGA implementation on data from 23 patients (198 seizures in total) shows a seizure detection sensitivity and specificity of 92.5% and 80.1%, respectively. Comparison to the state of the art is presented from system integration, the VLSI implementation, and the wireless communication perspectives.

Temporal lobe surgery and memory: Lessons, risks, and opportunities

Careful study of the clinical outcomes of temporal lobe epilepsy (TLE) surgery has greatly advanced our knowledge of the neuroanatomy of human memory. After early cases resulted in profound amnesia, the critical role of the hippocampus and associated medial temporal lobe (MTL) structures to declarative memory became evident. Surgical approaches quickly changed to become unilateral and later, to be more precise, potentially reducing cognitive morbidity. Neuropsychological studies following unilateral temporal lobe resection (TLR) have challenged early models, which simplified the lateralization of verbal and visual memory function. Diagnostic tests, including intracarotid sodium amobarbital procedure (WADA), structural magnetic resonance imaging (MRI), and functional neuroimaging (functional MRI (fMRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT)), can more accurately lateralize and localize epileptogenic cortex and predict memory outcomes from surgery. Longitudinal studies have shown that memory may even improve in seizure-free patients. From 70 years of experience with epilepsy surgery, we now have a richer understanding of the clinical, neuroimaging, and surgical predictors of memory decline-and improvement-after TLR. "Special Issue: Epilepsy & Behavior's 20th Anniversary".

Neural engineering: the process, applications, and its role in the future of medicine

OBJECTIVE

Recent advances in neural engineering have restored mobility to people with paralysis, relieved symptoms of movement disorders, reduced chronic pain, restored the sense of hearing, and provided sensory perception to individuals with sensory deficits.

APPROACH

This progress was enabled by the team-based, interdisciplinary approaches used by neural engineers. Neural engineers have advanced clinical frontiers by leveraging tools and discoveries in quantitative and biological sciences and through collaborations between engineering, science, and medicine. The movement toward bioelectronic medicines, where neuromodulation aims to supplement or replace pharmaceuticals to treat chronic medical conditions such as high blood pressure, diabetes and psychiatric disorders is a prime example of a new frontier made possible by neural engineering. Although one of the major goals in neural engineering is to develop technology for clinical applications, this technology may also offer unique opportunities to gain insight into how biological systems operate.

MAIN RESULTS

Despite significant technological progress, a number of ethical and strategic questions remain unexplored. Addressing these questions will accelerate technology development to address unmet needs. The future of these devices extends far beyond treatment of neurological impairments, including potential human augmentation applications. Our task, as neural engineers, is to push technology forward at the intersection of disciplines, while responsibly considering the readiness to transition this technology outside of the laboratory to consumer products.

SIGNIFICANCE

This article aims to highlight the current state of the neural engineering field, its links with other engineering and science disciplines, and the challenges and opportunities ahead. The goal of this article is to foster new ideas for innovative applications in neurotechnology.

[Mobile seizure monitoring in epilepsy patients]

Wearables are receiving much attention from both epilepsy patients and treating physicians, for monitoring of seizure frequency and warning of seizures. They are also of interest for the detection of seizure-associated risks of patients, for differential diagnosis of rare seizure types and prediction of seizure-prone periods. Accelerometry, electromyography (EMG), heart rate and further autonomic parameters are recorded to capture clinical seizure manifestations. Currently, a clinical use to document nocturnal motor seizures is feasible. In this review the available devices, data on the performance in the documentation of seizures, current options for clinical use and developments in data analysis are presented and critically discussed.

Neural stimulation systems for the control of refractory epilepsy: a review

Epilepsy affects nearly 1% of the world's population. A third of epilepsy patients suffer from a kind of epilepsy that cannot be controlled by current medications. For those where surgery is not an option, neurostimulation may be the only alternative to bring relief, improve quality of life, and avoid secondary injury to these patients. Until recently, open loop neurostimulation was the only alternative for these patients. However, for those whose epilepsy is applicable, the medical approval of the responsive neural stimulation and the closed loop vagal nerve stimulation systems have been a step forward in the battle against uncontrolled epilepsy. Nonetheless, improvements can be made to the existing systems and alternative systems can be developed to further improve the quality of life of sufferers of the debilitating condition. In this paper, we first present a brief overview of epilepsy as a disease. Next, we look at the current state of biomarker research in respect to sensing and predicting epileptic seizures. Then, we present the current state of open loop neural stimulation systems. We follow this by investigating the currently approved, and some of the recent experimental, closed loop systems documented in the literature. Finally, we provide discussions on the current state of neural stimulation systems for controlling epilepsy, and directions for future studies.

A Novel Approach for Responsive Neural Stimulator Implantation With Infraclavicular Placement of the Internal Pulse Generator

INTRODUCTION

The Responsive Neurostimulation System (RNS, Neuropace, Mountain View, California) has been proven to be effective at reducing seizures in patients with partial-onset epilepsy. The system incorporates a skull-mounted neurostimulator that requires a cranial incision for replacement. Although integral to the functioning of the system, in some circumstances, such as in the setting of infection, this can be disadvantageous. At present, there are no alternatives to cranial implantation of the RNS System.

METHODS

We describe a novel procedure enabling implantation of the neurostimulator within the chest wall, using components from a peripheral nerve stimulator. In a patient who achieved complete seizure freedom with the use of the RNS System, distant site implantation provided a viable means of continuing therapy in a setting where device explantation would have otherwise been inevitable as a result of cranial infection. We present continuous electrocorticographic data recorded from the device documenting the performance of the system with the subclavicular neurostimulator.

RESULTS

Band pass detection rates increased by 50%, while line length detection rates decreased by 50%. The number of detections decreased from 1046 to 846, with a resultant decrease in stimulations. Although there was some compromise of function due to the elevated noise floor, more than 2 yr following the procedure the patient remains free of seizures and infection.

CONCLUSION

The salvage procedure we describe offered an alternative therapeutic option in a patient with a complicated cranial wound issue, using heterogeneous components with marginal compromises in device functionality and no sacrifice in patient outcome.

Hardware Implementation of a Performance and Energy-optimized Convolutional Neural Network for Seizure Detection

We present for the first time a μW-power convolutional neural network for seizure detection running on a low-power microcontroller. On a dataset of 22 patients a median sensitivity of 100% is achieved. With a false positive rate of 20.7 fp/h and a short detection delay of 3.4 s it is suitable for the application in an implantable closed-loop device.

A Review of Neurostimulation for Epilepsy in Pediatrics

Neurostimulation for epilepsy refers to the application of electricity to affect the central nervous system, with the goal of reducing seizure frequency and severity. We review the available evidence for the use of neurostimulation to treat pediatric epilepsy, including vagus nerve stimulation (VNS), responsive neurostimulation (RNS), deep brain stimulation (DBS), chronic subthreshold cortical stimulation (CSCS), transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). We consider possible mechanisms of action and safety concerns, and we propose a methodology for selecting between available options. In general, we find neurostimulation is safe and effective, although any high quality evidence applying neurostimulation to pediatrics is lacking. Further research is needed to understand neuromodulatory systems, and to identify biomarkers of response in order to establish optimal stimulation paradigms.

Ultra-long-term subcutaneous home monitoring of epilepsy-490 days of EEG from nine patients

Objective

To explore the feasibility of home monitoring of epilepsy patients with a novel subcutaneous electroencephalography (EEG) device, including clinical implications, safety, and compliance via the first real‐life test.

Methods

We implanted a beta‐version of the 24/7 EEG SubQ (UNEEG Medical A/S, Denmark) subcutaneously in nine participants with temporal lobe epilepsy. Data on seizures, adverse events, compliance in using the device, and use of antiepileptic drugs (AEDs) were collected. EEG was recorded for up to 3 months, and all EEG data were reviewed visually to identify electrographic seizures. These were descriptively compared to seizure counts and AED changes reported in diaries from the same period.

Results

Four hundred ninety days of EEG and 338 electrographic seizures were collected. Eight participants completed at least 9 weeks of home monitoring, while one cancelled participation after 4 weeks due to postimplantation soreness. In total, 13 cases of device‐related adverse events were registered, none of them serious. Recordings obtained from the device covered 73% of the time, on average (range 45%‐91%). Descriptively, electrographic seizure counts were substantially different from diary seizure counts. We uncovered several cases of underreporting and revealed important information on AED response. Electrographic seizure counts revealed circadian distributions of seizures not visible from seizure diaries.

Significance

The study shows that home monitoring for up to 3 months with a subcutaneous EEG device is feasible and well tolerated. No serious adverse device‐related events were reported. An objective seizure count can be derived, which often differs substantially from self‐reported seizure counts. Larger clinical trials quantifying the benefits of objective seizure counting should be a priority for future research as well as development of algorithms for automated review of data.

A Novel Robotic-Assisted Technique to Implant the Responsive Neurostimulation System

BACKGROUND

The responsive neurostimulation system (RNS) (NeuroPace Inc, Mountain View, California) was approved as an adjunctive therapy for medically refractory focal epilepsy. RNS detects epileptiform patterns and delivers electrical stimulation to abort seizures.

OBJECTIVE

To describe a novel technique of RNS lead implantation using robotic-assisted targeting of ictal-onset zones based on stereoelectroencephalography (sEEG) localization. Secondary objectives are to report the accuracy of robotic-assisted lead implantation using the ROSA robot as well as to report the clinical outcome achieved after RNS implantation by this method.

METHODS

A total of 16 patients with medically refractory focal epilepsy underwent sEEG implantation for ictal-onset localization followed by robotic RNS implantation. The electrode most correlative with ictal onset on sEEG was chosen as the target for the RNS electrode. Seizure control was measured at 6-mo and 1-yr follow-up. Ictal-onset electrocorticography (ECoG) data from RNS were compared with ictal onset from sEEG leads based on calculations of lead target to actual lead location from the ROSA robot.

RESULTS

At 6-mo follow-up, the average percent seizure reduction was 82% based upon self-reported seizure diaries. At 1-yr follow-up, 8 patients had an average of 90% seizure reduction. The location of seizure onset from ECoG data show similar onset from sEEG leads within 0.165-mm discrepancy.

CONCLUSION

The ROSA robot provides an ideal method for targeting subcortical ictal-onset zones. This method of RNS lead implantation achieves high accuracy and is associated with favorable clinical outcomes.

Multiple Subpial Transections for Medically Refractory Epilepsy: A Disaggregated Review of Patient-Level Data

BACKGROUND

Multiple subpial transections (MST) are a treatment for seizure foci in nonresectable eloquent areas.

OBJECTIVE

To systematically review patient-level data regarding MST.

METHODS

Studies describing patient-level data for MST procedures were extracted from the Medline and PubMed databases, yielding a synthetic cohort of 212 patients from 34 studies. Data regarding seizure outcome, patient demographics, seizure type, surgery type, and complications were extracted and analyzed.

RESULTS

Seizure freedom was achieved in 55.2% of patients undergoing MST combined with resection, and 23.9% of patients undergoing MST alone. Significant predictors for seizure freedom were a temporal lobe focus (odds ratio 4.9; 95% confidence interval 1.71, 14.3) and resection of portions of the focus, when feasible (odds ratio 3.88; 95% confidence interval 2.02, 7.45). Complications were frequent, with transient mono- or hemiparesis affecting 19.8% of patients, transient dysphasia 12.3%, and permanent paresis or dysphasia in 6.6% and 1.9% of patients, respectively.

CONCLUSION

MST is an effective treatment for refractory epilepsy in eloquent cortex, with greater chances of seizure freedom when portions of the focus are resected in tandem with MST. The reported rates of seizure freedom with MST are higher than those of existing neuromodulatory therapies, such as vagus nerve stimulation, deep brain stimulation, and responsive neurostimulation, though these latter therapies are supported by randomized-controlled trials, while MST is not. The reported complication rate of MST is higher than that of resection and neuromodulatory therapies. MST remains a viable option for the treatment of eloquent foci, provided a careful risk-benefit analysis is conducted.

Responsive neurostimulation targeting anterior thalamic nucleus in generalized epilepsy

Responsive neurostimulation (RNS) has emerged as an adjunctive treatment modality for patients with intractable focal epilepsy who are not surgical candidates or have more than one ictal onset focus. We report a 34‐year‐old patient with intractable, childhood‐onset, genetic generalized epilepsy (GGE) with tonic, atonic, myoclonic and absence seizures treated with RNS. Strip electrodes over the right posterior frontal cortex and depth electrodes placed in the right anterior nucleus were used for event detection and responsive stimulation. Two‐year follow‐up revealed 90–95% clinical seizure reduction. This case suggests that refractory GGE may be effectively treated with RNS targeting thalamocortical networks.

Unsupervised Learning of Spatiotemporal Interictal Discharges in Focal Epilepsy

BACKGROUND

Interictal epileptiform discharges are an important biomarker for localization of focal epilepsy, especially in patients who undergo chronic intracranial monitoring. Manual detection of these pathophysiological events is cumbersome, but is still superior to current rule-based approaches in most automated algorithms.

OBJECTIVE

To develop an unsupervised machine-learning algorithm for the improved, automated detection and localization of interictal epileptiform discharges based on spatiotemporal pattern recognition.

METHODS

We decomposed 24 h of intracranial electroencephalography signals into basis functions and activation vectors using non-negative matrix factorization (NNMF). Thresholding the activation vector and the basis function of interest detected interictal epileptiform discharges in time and space (specific electrodes), respectively. We used convolutive NNMF, a refined algorithm, to add a temporal dimension to basis functions.

RESULTS

The receiver operating characteristics for NNMF-based detection are close to the gold standard of human visual-based detection and superior to currently available alternative automated approaches (93% sensitivity and 97% specificity). The algorithm successfully identified thousands of interictal epileptiform discharges across a full day of neurophysiological recording and accurately summarized their localization into a single map. Adding a temporal window allowed for visualization of the archetypal propagation network of these epileptiform discharges.

CONCLUSION

Unsupervised learning offers a powerful approach towards automated identification of recurrent pathological neurophysiological signals, which may have important implications for precise, quantitative, and individualized evaluation of focal epilepsy.

Chronic subthreshold cortical stimulation and stimulation-related EEG biomarkers for focal epilepsy

Brain stimulation offers an alternative to focal resection for the treatment of focal drug-resistant epilepsy. Chronic subthreshold cortical stimulation is an individualized biomarker-informed open-loop continuous electrical stimulation approach targeting the seizure onset zone and surrounding areas. Before permanent implantation, trial stimulation is performed during invasive monitoring to assess stimulation efficacy as well as to optimize stimulation location and parameters by modifying interictal EEG biomarkers. We present clinical and neurophysiological results from a retrospective analysis of 21 patients, showing a median percent reduction in seizure frequency of 100% and responder rate of 89% with a median follow-up of 27 months. About 40% of patients were free of disabling seizures for a 12-month period or longer. We find that stimulation-induced decreases in delta (1–4 Hz) power and increases in alpha and beta (8–20 Hz) power during trial stimulation correlate with improved long-term clinical outcomes. These results suggest chronic subthreshold cortical stimulation may be an effective alternative approach to treating focal drug-resistant epilepsy and that short-term stimulation-related changes in spectral power may be a useful interictal biomarker and relate to long-term clinical outcome.

Let's talk SUDEP

Sudden unexplained death in epilepsy (SUDEP) is a devastating complication of epilepsy which was under-recognized in the recent past despite its clear importance. In this review, we examine the definition of SUDEP, revise current pathophysiological theories, discuss risk factors and preventative measures, disclose tools for appraising the SUDEP risk, and last but not least dwell upon announcing and explaining the SUDEP risk to the patients and their caretakers. We aim to aid the clinicians in their responsibility of knowing SUDEP, explaining the SUDEP risk to their patients in a reasonable and sensible way and whenever possible, preventing SUDEP. Future studies are definitely needed to increase scientific knowledge and awareness related to this prioritized topic with malign consequences.

Practice trends and the outcome of neuromodulation therapies in epilepsy: A single-center study

Neuromodulation therapies (VNS, RNS, and DBS) can improve seizure control in persons with epilepsy. However, there is a significant service gap in integrating these therapies in clinical care. Our epilepsy center has established an epilepsy neuromodulation clinic to improve access to patients, communication with referring physicians, track outcome and train future providers in programming neuromodulation devices. We report the (a) treatment outcome of the available neuromodulation therapies (ie, reduction in seizure frequency over 6-12 months follow-up); and (b) demonstrate the benefit of the specialized clinic (rapid titration, continuity of care, superior access for patient and vendors). In this single-center, retrospective study, forty-three adults (VNS = 27; RNS = 16) with drug-resistant epilepsy were followed in the clinic during the 19 months study period. About 44-69% of patients reported > 60% decrease in seizure. All patients were scheduled in the clinic within 2-4 weeks, and stimulations were optimized rapidly. About 40% of patients participated in research while 28% were referred for additional diagnostic studies. Nineteen students and fellows were trained in programming neurostimulator. Epilepsy neuromodulation clinic can serve as an optimal solution for patients as well as providers due to rapid access, better continuity of care, higher recruitment for research studies, and training health professionals.

Precision electronic medicine in the brain

Periodically throughout history developments from adjacent fields of science and technology reach a tipping point where together they produce unparalleled advances, such as the Allen Brain Atlas and the Human Genome Project. Today, research focused at the interface between the nervous system and electronics is not only leading to advances in fundamental neuroscience, but also unlocking the potential of implants capable of cellular-level therapeutic targeting. Ultimately, these personalized electronic therapies will provide new treatment modalities for neurodegenerative and neuropsychiatric illness; powerful control of prosthetics for restorative function in degenerative diseases, trauma and amputation; and even augmentation of human cognition. Overall, we believe that emerging advances in tissue-like electronics will enable minimally invasive devices capable of establishing a stable long-term cellular neural interface and providing long-term treatment for chronic neurological conditions.

Functional Frequency Discrimination From Cortical Somatosensory Stimulation in Humans

Recently, efforts to produce artificial sensation through cortical stimulation of primary somatosensory cortex (PSC) in humans have proven safe and reliable. Changes in stimulation parameters like frequency and amplitude have been shown to elicit different percepts, but without clearly defined psychometric profiles. This study investigates the functionally useful limits of frequency changes on the percepts felt by three epilepsy patients with subdural electrocorticography (ECoG) grids. Subjects performing a hidden target task were stimulated with parameters of constant amplitude, pulse-width, and pulse-duration, and a randomly selected set of two frequencies (20, 30, 40, 50, 60, and 100 Hz). They were asked to decide which target had the “higher” frequency. Objectively, an increase in frequency differences was associated with an increase in perceived intensity. Reliable detection of stimulation occurred at and above 40 Hz with a lower limit of detection around 20 Hz and a just-noticeable difference estimated at less than 10 Hz. These findings suggest that frequency can be used as a reliable, adjustable parameter and may be useful in establishing settings and thresholds of functionality in future BCI systems.

Multi-feature localization of epileptic foci from interictal, intracranial EEG

OBJECTIVE

When considering all patients with focal drug-resistant epilepsy, as high as 40-50% of patients suffer seizure recurrence after surgery. To achieve seizure freedom without side effects, accurate localization of the epileptogenic tissue is crucial before its resection. We investigate an automated, fast, objective mapping process that uses only interictal data.

METHODS

We propose a novel approach based on multiple iEEG features, which are used to train a support vector machine (SVM) model for classification of iEEG electrodes as normal or pathologic using 30 min of inter-ictal recording.

RESULTS

The tissue under the iEEG electrodes, classified as epileptogenic, was removed in 17/18 excellent outcome patients and was not entirely resected in 8/10 poor outcome patients. The overall best result was achieved in a subset of 9 excellent outcome patients with the area under the receiver operating curve = 0.95.

CONCLUSION

SVM models combining multiple iEEG features show better performance than algorithms using a single iEEG marker. Multiple iEEG and connectivity features in presurgical evaluation could improve epileptogenic tissue localization, which may improve surgical outcome and minimize risk of side effects.

SIGNIFICANCE

In this study, promising results were achieved in localization of epileptogenic regions by SVM models that combine multiple features from 30 min of inter-ictal iEEG recordings.

Novel therapies for epilepsy in the pipeline

Despite the availability of many antiepileptic drugs (AEDs) (old and newly developed) and, as recently suggested, their optimization in the treatment of patients with uncontrolled seizures, more than 30% of patients with epilepsy continue to experience seizures and have drug-resistant epilepsy; the management of these patients represents a real challenge for epileptologists and researchers. Resective surgery with the best rates of seizure control is not an option for all of them; therefore, research and discovery of new methods of treating resistant epilepsy are of extreme importance. In this article, we will discuss some innovative approaches, such as P-glycoprotein (P-gp) inhibitors, gene therapy, stem cell therapy, traditional and novel antiepileptic devices, precision medicine, as well as therapeutic advances in epileptic encephalopathy in children; these treatment modalities open up new horizons for the treatment of patients with drug-resistant epilepsy.

Precursors of seizures due to specific spatial-temporal modifications of evolving large-scale epileptic brain networks

Knowing when, where, and how seizures are initiated in large-scale epileptic brain networks remains a widely unsolved problem. Seizure precursors – changes in brain dynamics predictive of an impending seizure – can now be identified well ahead of clinical manifestations, but either the seizure onset zone or remote brain areas are reported as network nodes from which seizure precursors emerge. We aimed to shed more light on the role of constituents of evolving epileptic networks that recurrently transit into and out of seizures. We constructed such networks from more than 3200 hours of continuous intracranial electroencephalograms recorded in 38 patients with medication refractory epilepsy. We succeeded in singling out predictive edges and predictive nodes. Their particular characteristics, namely edge weight respectively node centrality (a fundamental concept of network theory), from the pre-ictal periods of 78 out of 97 seizures differed significantly from the characteristics seen during inter-ictal periods. The vast majority of predictive nodes were connected by most of the predictive edges, but these nodes never played a central role in the evolving epileptic networks. Interestingly, predictive nodes were entirely associated with brain regions deemed unaffected by the focal epileptic process. We propose a network mechanism for a transition into the pre-seizure state, which puts into perspective the role of the seizure onset zone in this transition and highlights the necessity to reassess current concepts for seizure generation and seizure prevention.

Robust closed-loop control of spike-and-wave discharges in a thalamocortical computational model of absence epilepsy

In this paper, we investigate the abatement of spike-and-wave discharges in a thalamocortical model using a closed-loop brain stimulation method. We first explore the complex states and various transitions in the thalamocortical computational model of absence epilepsy by using bifurcation analysis. We demonstrate that the Hopf and double cycle bifurcations are the key dynamical mechanisms of the experimental observed bidirectional communications during absence seizures through top-down cortical excitation and thalamic feedforward inhibition. Then, we formulate the abatement of epileptic seizures to a closed-loop tracking control problem. Finally, we propose a neural network based sliding mode feedback control system to drive the dynamics of pathological cortical area to track the desired normal background activities. The control system is robust to uncertainties and disturbances, and its stability is guaranteed by Lyapunov stability theorem. Our results suggest that the seizure abatement can be modeled as a tracking control problem and solved by a robust closed-loop control method, which provides a promising brain stimulation strategy.

Early Detection of Human Epileptic Seizures Based on Intracortical Microelectrode Array Signals

OBJECTIVE

We examine, for the first time, the use of intracortical microelectrode array (MEA) signals for early detection of human epileptic seizures.

METHODS

4×4 mm² 96-channel-MEA recordings were obtained during neuro-monitoring preceding resective surgery in five participants. The participant-specific seizure-detection framework consisted of: first, feature extraction from local field potentials (LFPs) and multiunit activity (MUA); second, nonlinear cost-sensitive support vector machine (SVM) classification of ictal and interictal states based on LFP, MUA, and combined LFP-MUA (a SVM was trained for each participant separately); and third, Kalman filter postprocessing of SVM scoring functions. Performance was assessed on data including 17 seizures and 39.0 h interictal and preictal recordings.

RESULTS

The use of combined LFP-MUA features resulted in 100% sensitivity with short detection latency (average: 2.7 s; median: 2.5 s) and five false alarms (0.13/h). The average detection performance based on the area under the receiver operating characteristic corresponded to 0.97. Importantly, technically false alarms were related to epileptiform activity, subclinical seizures, and recording artifacts. Extreme gradient boosting classifiers ranked features based on LFP spectral coherence or MUA count among the top features for seizures characterized by spike-wave complexes, whereas features related to LFP power spectra were ranked higher for seizures characterized by sustained gamma LFP oscillations.

CONCLUSION

The combination of intracortical LFP and MUA signals may allow reliable detection of human epileptic seizures by improving latency and false alarm rate.

SIGNIFICANCE

Intracortical MEAs provide promising signals for closed-loop seizure-control systems based on seizure early-detection in people with pharmacologically resistant epilepsies.

Deep Brain Stimulation and Drug-Resistant Epilepsy: A Review of the Literature

Introduction: Deep brain stimulation is a safe and effective neurointerventional technique for the treatment of movement disorders. Electrical stimulation of subcortical structures may exert a control on seizure generators initiating epileptic activities. The aim of this review is to present the targets of the deep brain stimulation for the treatment of drug-resistant epilepsy. Methods: We performed a structured review of the literature from 1980 to 2018 using Medline and PubMed. Articles assessing the impact of deep brain stimulation on seizure frequency in patients with DRE were selected. Meta-analyses, randomized controlled trials, and observational studies were included. Results: To date, deep brain stimulation of various neural targets has been investigated in animal experiments and humans. This article presents the use of stimulation of the anterior and centromedian nucleus of the thalamus, hippocampus, basal ganglia, cerebellum and hypothalamus. Anterior thalamic stimulation has demonstrated efficacy and there is evidence to recommend it as the target of choice. Conclusion: Deep brain stimulation for seizures may be an option in patients with drug-resistant epilepsy. Anterior thalamic nucleus stimulation could be recommended over other targets.

Deep brain stimulation of the anterior nucleus of the thalamus for drug-resistant epilepsy

Despite the use of first-choice anti-epileptic drugs and satisfactory seizure outcome rates after resective epilepsy surgery, a considerable percentage of patients do not become seizure free. ANT-DBS may provide for an alternative treatment option in these patients. This literature review discusses the rationale, mechanism of action, clinical efficacy, safety, and tolerability of ANT-DBS in drug-resistant epilepsy patients. A review using systematic methods of the available literature was performed using relevant databases including Medline, Embase, and the Cochrane Library pertaining to the different aspects ANT-DBS. ANT-DBS for drug-resistant epilepsy is a safe, effective and well-tolerated therapy, where a special emphasis must be given to monitoring and neuropsychological assessment of both depression and memory function. Three patterns of seizure control by ANT-DBS are recognized, of which a delayed stimulation effect may account for an improved long-term response rate. ANT-DBS remotely modulates neuronal network excitability through overriding pathological electrical activity, decrease neuronal cell loss, through immune response inhibition or modulation of neuronal energy metabolism. ANT-DBS is an efficacious treatment modality, even when curative procedures or lesser invasive neuromodulative techniques failed. When compared to VNS, ANT-DBS shows slightly superior treatment response, which urges for direct comparative trials. Based on the available evidence ANT-DBS and VNS therapies are currently both superior compared to non-invasive neuromodulation techniques such as t-VNS and rTMS. Additional in-vivo research is necessary in order to gain more insight into the mechanism of action of ANT-DBS in localization-related epilepsy which will allow for treatment optimization. Randomized clinical studies in search of the optimal target in well-defined epilepsy patient populations, will ultimately allow for optimal patient stratification when applying DBS for drug-resistant patients with epilepsy.

Treatment of drug-resistant epilepsy in patients with periventricular nodular heterotopia using RNS® System: Efficacy and description of chronic electrophysiological recordings

OBJECTIVES

Describe changes in clinical seizure frequency and electrophysiological data recorded in patients with medically-intractable seizures and periventricular nodular heterotopias (PVNH) treated with the RNS® System (NeuroPace, Inc., Mountain View, CA).

METHODS

Clinical seizures from eight patients (mean follow-up of 10.1 years) were analyzed pre- and post-treatment. Chronic ambulatory electrocorticograms (ECoGs) recorded from PVNHs, hippocampus and neocortex were evaluated to identify the earliest electrographic seizure onset type, pattern of spread, and interictal characteristics.

RESULTS

Mean reduction in disabling seizures was 85.7 % (n = 8); seven patients had >50% seizure reduction and two were seizure-free in the final year of analysis. Seizure rate showed a progressive reduction over the course of the study with the highest rate of improvement in the first two to three years after implantation. Four of seven patients with one PVNH lead and a second lead in the hippocampus or neocortex had some electrographic seizures first recorded at either lead location, suggesting two foci or seizure propagation patterns. Low voltage fast type activity was the prominent seizure onset pattern. Interictal ECoG power was lower in PVNH than hippocampus.

CONCLUSIONS

RNS® System treatment substantially reduced clinical seizure frequency in patients with PVNH. Analysis of ictal ECoG records suggests PVNH may be involved in seizure generation.

SIGNIFICANCE

Chronic ECoG recordings suggest PVNH tissue can actively participate in epileptogenic networks. Direct brain-responsive neurostimulation is a safe and effective treatment option in such patients, progressively reducing seizure rate over a period of years.

Comparison and Selection of Current Implantable Anti-Epileptic Devices

Implantable neural stimulators represent an advanced treatment adjunct to medication for pharmacoresistant epilepsy and alternative for patients that are not good candidates for resective surgery. Three treatment modalities are currently FDA-approved: vagus nerve stimulation, responsive neurostimulation, and deep brain stimulation. These devices were originally trialed in very similar patient populations with focal epilepsy, but head-to-head comparison trials have not been performed. As such, device selection may be challenging due to large overlaps in clinical indications and efficacy. Here we will review the data reported in the original pivotal clinical trials as well as long-term experience with these technologies. We will highlight differences in their features and mechanisms of action which may help optimize device selection on a case-by-case basis.